sbc8560: define eth0 and eth1 instead of eth1 and eth2

sbc8560: define eth0 and eth1 instead of eth1 and eth2

The existing config doesn't define CONFIG_HAS_ETH0, and so the
fdt support doesn't update the zeros in the dtb local-mac with
real data from the u-boot env.  Since the existing config is
tailored to just two interfaces, get rid of the ETH2 definitions
at the same time.

Also don't include any end user specific data into the environment
by default -- things like MAC address, network parameters etc. need
to come from the end user.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>